Luminous display unit

ABSTRACT

A luminous display unit  10.0  has plural segments  21   a  to  21   g  (light emitting portions) by using a self light emitting element reduced in light emitting luminance in accordance with a light emitting time and has differences in light emitting time in their light emitting portions. The light emitting luminance of a light emitting portion having a long light emitting time and the light emitting luminance of a light emitting portion having a short light emitting time at a using time of the luminous display unit  100  are set to be different from each other from the first so as not to recognize a difference in light emitting luminance caused between both the light emitting portions at said using time.

TECHNICAL FIELD

This invention relates to a luminous display unit e.g., a luminousdisplay unit using a self light emitting element such as an organicelectroluminescence element (OLED), a fluorescent display tube, a lightemitting diode (LED), etc.

BACKGROUND OF THE INVENTION

As shown in FIG. 5, an OLED 5 has at least an anode 2 constructed by atransparent electroconductive material such as indium, tin, oxide (ITO),etc., an organic layer 3 constructed by one or more layers (constructedby at least a single layer structure of an organic light emitting layer,or a multilayer structure in which a positive hole injecting layer, apositive hole transport layer, an electronic transport layer and anelectronic injecting layer, etc. are laminated and formed from an anodeside in accordance with the organic light emitting layer), and a cathode4 constructed by a metallic electroconductive material such as aluminum(Al), etc. on a transparent substrate 1. For example, this OLED 5 isknown in Japanese Patent Publication No. 32307/1994. The OLED 5 can emitlight in a predetermined desirable pattern by shapes of the anode 2 andthe cathode 4. Further, it is possible to perform display in constantelectric current driving from a direct current power source vcc fromseveral volts to several ten volts.

When a luminous display unit 100 using such an OLED 5 is utilized as adigital type distance recorder of a display unit for a vehicle, as shownin FIG. 6, the anode 2 is divided into seven segments 2 a to 2 garranged in an 8-shape so that Arabic numerals “0” to “9” areartificially displayed. Numerals of plural digits can be displayed byarranging a plurality of such anodes in a transversal direction. Forexample, such a construction is known in Japanese Patent Laid-Open No.106887/1997.

FIG. 6 shows an example of six-digit display able to display “000000” to“999999”.

It is known that light emitting intensity in each of the segments 2 a to2 g is reduced in accordance with a light emitting time. For example,when the light emitting time is ten thousand hours, light emittingluminance is reduced to about 50% of the original light emittingluminance.

If each of the segments 2 a to 2 g emits light for a uniform lightemitting time, the reductions in light emitting luminance are uniform.Therefore, no difference in light emitting luminance between therespective segments 2 a to 2 g is almost caused irrespective of thelength of a using time of the luminous display unit.

However, when there is a large difference in light emitting time, thedifference in light emitting luminance is increased. Accordingly, as theusing time of the luminous display unit is lengthened, this differenceis enlarged. When these segments 2 a to 2 g simultaneously emit light,there is a case in which a feeling of physical disorder is felt by thedifference in light emitting luminance. In such a state, goods propertyis greatly damaged.

In the case of the digital type distance recorder, light emittingfrequency of each of the segments 2 a to 2 g in the display of numerals“0” to “9” of ten kinds in each digit is provided as shown in FIG. 7. InFIG. 7, the segment 2 c has a maximum light emitting frequency of ninetimes, and the segment 2 e has a minimum light emitting frequency offour times. When it is supposed that the light emitting time of each ofthe numerals “0” to “9” is uniform, the light emitting time of thesegment 2 c is 2.25 times the light emitting time of the segment 2 e.

Accordingly, although it is the same digit, the light emitting luminanceof the segment 2 c is rapidly reduced in comparison with the lightemitting luminance of the segment 2 e. When this difference in lightemitting luminance is increased to such an extent that this differencecan be recognized, a problem exists in that a user has a feeling ofphysical disorder. When the difference in light emitting luminance isequal to or greater than a value corresponding to 30% of a higher lightemitting luminance among these light emitting luminances, it isconfirmed by an experiment of the present inventors, etc. that thedifference in light emitting luminance between both the segments can berecognized.

When no numeral “0” is displayed on an upper digit side, i.e., when“120” having no numerals “0” in upper three digits is displayed as ablank display instead of “000120” displaying numerals “0” in the upperthree digits in display of the numeral “120” (in the case of a so-calledleading zero suppress display), the light emitting time in the upperdigit is shortened in comparison with a lower digit so that a problemsimilar to the above problem is caused.

Disclosure of the Invention

The present invention resides in a luminous display unit having plurallight emitting portions by using a self light emitting element reducedin light emitting luminance in accordance with a light emitting time andhaving differences in light emitting time in their light emittingportions, and characterized in that, when a light emitting mode in saidlight emitting portions is regularly determined, said light emittingtime is presumed from light emitting frequencies of said light emittingportions calculated from said light emitting mode, and the lightemitting luminances are set to be different from each other from thefirst in a light emitting portion having a large light emittingfrequency and a light emitting portion having a small light emittingfrequency at a using time of said luminous display unit so as not torecognize a difference in light emitting luminance caused between boththe light emitting portions at said using time. For example, each ofluminous display units 100, 110 has plural segments 21 a to 21 g (lightemitting portions) by using an OLED (a self light emitting element)reduced in light emitting luminance in accordance with a light emittingtime and has differences in light emitting time in their light emittingportions. When a light emitting mode in the segments 21 a to 21 g isregularly determined, the light emitting time of each of the segments 21a to 21 g is presumed from light emitting frequencies of the segments 21a to 21 g calculated from this light emitting mode, and the lightemitting luminances are set to be different from each other from thefirst in a light emitting portion having a large light emittingfrequency and a light emitting portion having a small light emittingfrequency at a using time of each of the luminous display units 100, 110so as not to recognize a difference in light emitting luminance causedbetween both the light emitting portions at the using time. Thus, thegeneration of a large difference in light emitting luminance of each ofthe segments 21 a to 21 g is prevented at the using time of each of theluminous display units 100, 110 so that goods property can bemaintained.

The present invention also resides in a luminous display unit havingplural light emitting portions by using a self light emitting elementreduced in light emitting luminance in accordance with a light emittingtime and having differences in light emitting time in their lightemitting portions, and characterized in that, when a light emitting modein said light emitting portions is regularly determined, said lightemitting time is presumed from light emitting frequencies of said lightemitting portions calculated from said light emitting mode, and thelight emitting luminances are set to be different from each other fromthe first in a light emitting portion having a large light emittingfrequency and a light emitting portion having a small light emittingfrequency at a using time of said luminous display unit such that adifference in light emitting luminance caused between both the lightemitting portions lies within 30% of a high light emitting luminanceamong the light emitting luminances at said using time. For example,each of luminous display units 100, 110 has plural segments 21 a to 21 g(light emitting portions) by using an OLED (a self light emittingelement) reduced in light emitting luminance in accordance with a lightemitting time and has differences in light emitting time in their lightemitting portions. When a light emitting mode in the segments 21 a to 21g is regularly determined, the light emitting time of each of thesegments 21 a to 21 g is presumed from light emitting frequencies of thesegments 21 a to 21 g calculated from this light emitting mode, and thelight emitting luminances are set to be different from each other fromthe first in a light emitting portion having a large light emittingfrequency and a light emitting portion having a small light emittingfrequency at a using time of each of the luminous display units 100, 110such that a difference in light emitting luminance caused between boththe light emitting portions lies within 30% of a high light emittingluminance among the light emitting luminances at said using time. Thus,the generation of a large difference in light emitting luminance of eachof the segments 21 a to 21 g is prevented at the using time of each ofthe luminous display units 100, 110 so that goods property can bemaintained.

The present invention also resides in a luminous display unit havingplural light emitting portions by using a self light emitting elementreduced in light emitting luminance in accordance with a light emittingtime and having differences in light emitting time in their lightemitting portions, and characterized in that, when a light emitting modein said light emitting portions is regularly determined, said lightemitting time is presumed from light emitting frequencies of said lightemitting portions calculated from said light emitting mode, and thelight emitting luminance of a light emitting portion having a smalllight emitting frequency is set to be lower than that of a lightemitting portion having a large light emitting frequency from the firstwith respect to the light emitting portion having a large light emittingfrequency and the light emitting portion having a small light emittingfrequency at a using time of said luminous display unit such that adifference in light emitting luminance caused between both the lightemitting portions lies within 30% of a high light emitting luminanceamong the light emitting luminances at said using time. For example,each of luminous display units 100, 110 has plural segments 21 a to 21 g(light emitting portions) by using an OLED (a self light emittingelement) reduced in light emitting luminance in accordance with a lightemitting time and has differences in light emitting time in their lightemitting portions. When a light emitting mode in the segments 21 a to 21g is regularly determined, the light emitting time of each of thesegments 21 a to 21 g is presumed from light emitting frequencies of thesegments 21 a to 21 g calculated from this light emitting mode, and thelight emitting luminance of a light emitting portion having a smalllight emitting frequency is set to be lower than that of a lightemitting portion having a large light emitting frequency from the firstwith respect to the light emitting portion having a large light emittingfrequency and the light emitting portion having a small light emittingfrequency at a using time of each of the luminous display units 100, 110such that a difference in light emitting luminance caused between boththe light emitting portions lies within 30% of a high light emittingluminance among the light emitting luminances at said using time. Thus,the generation of a large difference in light emitting luminance of eachof the segments 21 a to 21 g is prevented at the using time of each ofthe luminous display units 100, 110 so that goods property can bemaintained.

The present invention also resides in a luminous display unit havingplural light emitting portions by using a self light emitting elementreduced in light emitting luminance in accordance with a light emittingtime and having differences in light emitting time in their lightemitting portions, and characterized in that the light emittingluminance of a light emitting portion having a long light emitting timeand the light emitting luminance of a light emitting portion having ashort light emitting time at a using time of said luminous display unitare set to be different from each other from the first so as not torecognize a difference in light emitting luminance caused between boththe light emitting portions at said using time. For example, each ofluminous display units 100, 110 has plural segments 21 a to 21 g (lightemitting portions) by using an OLED (a self light emitting element)reduced in light emitting luminance in accordance with a light emittingtime and has differences in light emitting time in their light emittingportions. The light emitting luminance of a light emitting portionhaving a long light emitting time and the light emitting luminance of alight emitting portion having a short light emitting time at a usingtime of each of the luminous display units 100, 110 are set to bedifferent from each other from the first so as not to recognize adifference in light emitting luminance caused between both the lightemitting portions at said using time. Thus, the generation of a largedifference in light emitting luminance of each of the segments 21 a to21 g is prevented at the using time of each of the luminous displayunits 100, 110 so that goods property can be maintained.

The present invention also resides in a luminous display unit havingplural light emitting portions by using a self light emitting elementreduced in light emitting luminance in accordance with a light emittingtime and having differences in light emitting time in their lightemitting portions, and characterized in that the light emittingluminance of a light emitting portion having a long light emitting timeand the light emitting luminance of a light emitting portion having ashort light emitting time at a using time of said luminous display unitare set to be different from each other from the first such that adifference in light emitting luminance caused between both the lightemitting portions lies within 30% of a high light emitting luminanceamong the light emitting luminances at said using time. For example,each of luminous display units 100, 110 has plural segments 21 a to 21 g(light emitting portions) by using an OLED (a self light emittingelement) reduced in light emitting luminance in accordance with a lightemitting time and has differences in light emitting time in their lightemitting portions. The light emitting luminance of a light emittingportion having a long light emitting time and the light emittingluminance of a light emitting portion having a short light emitting timeat a using time of each of the luminous display units 100, 110 are setto be different from each other from the first such that a difference inlight emitting luminance caused between the light emitting portions lieswithin 30% of a high light emitting luminance among the light emittingluminances at said using time. Thus, the generation of a largedifference in light emitting luminance of each of the segments 21 a to21 g is prevented at the using time of each of the luminous displayunits 100, 110 so that goods property can be maintained.

Further, the present invention resides in a luminous display unit havingplural light emitting portions by using a self light emitting elementreduced in light emitting luminance in accordance with a light emittingtime and having differences in light emitting time in their lightemitting portions, and characterized in that the light emittingluminance of a light emitting portion having a short light emitting timeis set to be lower than that of a light emitting portion having a longlight emitting time from the first with respect to the light emittingportion having a long light emitting time and the light emitting portionhaving a short light emitting time at a using time of said luminousdisplay unit such that a difference in light emitting luminance causedbetween both the light emitting portions lies within 30% of a high lightemitting luminance among the light emitting luminances at said usingtime. For example, each of luminous display units 100, 110 has pluralsegments 21 a to 21 g (light emitting portions) by using an OLED (a selflight emitting element) reduced in light emitting luminance inaccordance with a light emitting time and has differences in lightemitting time in their light emitting portions. The light emittingluminance of a light emitting portion having a short light emitting timeis set to be lower than that of a light emitting portion having a longlight emitting time from the first with respect to the light emittingportion having a long light emitting time and the light emitting portionhaving a short light emitting time at a using time of each of theluminous display units 100, 110 such that a difference in light emittingluminance caused between both the light emitting portions lies within30% of a high light emitting luminance among the light emittingluminances at said using time. Thus, the generation of a largedifference in light emitting luminance of each of the segments 21 a to21 g is prevented at the using time of each of the luminous displayunits 100, 110 so that goods property can be maintained.

The luminous display unit is particularly characterized in that saidself light emitting element is an organic electroluminescence element.For example, in the case of the OLED as a light emitting element, achange in light emitting luminance according to the light emitting time(light emitting frequency) is notable, and the generation of a largedifference in light emitting luminance of each of the segments 21 a to21 g is prevented at the using time of each of the luminous displayunits 100, 110 so that goods property can be maintained.

The luminous display unit is particularly characterized in that saidluminous display unit is a display unit for a vehicle displaying anumeral of plural digits. For example, in the case of the display unitfor a vehicle displaying a numeral of plural digits as the luminousdisplay units 100, 110, the change in light emitting luminance isnotable since it is expected that the display unit is used for a longperiod such as several hundred thousand Km or several years. In thiscase, the generation of a large difference in light emitting luminanceof each of the segments 21 a to 21 g is also prevented at the using timeof each of the luminous display units 100, 110 so that goods propertycan be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a first embodiment of the present invention.

FIG. 2 is a circuit diagram in the above embodiment.

FIG. 3 is a characteristic graph for explaining a light emitting statein the above embodiment.

FIG. 4 is a plan view of a second embodiment of the present invention.

FIG. 5 is a cross-sectional view showing the structure of an organicelectroluminescence element.

FIG. 6 is a front view of a luminous display unit in the prior art.

FIG. 7 is a time series view for explaining a light emitting state inthe prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be explained on the basis of embodimentsshown in the accompanying drawings, but the same portions as the aboveprior art, or portions corresponding to those in the above prior art aredesignated by the same reference numerals, and their detailedexplanations are omitted here.

FIGS. 1 to 3 relate to a first embodiment of the present invention.Reference numeral 100 designates a luminous display unit in the presentinvention which is a digital type distance recorder as a display unitfor a vehicle using an OLED 5 (see FIG. 5).

An anode 2 (see FIG. 5) is divided into six groups 21 to 26. The group21 is divided into seven segments 21 a to 21 g as light emittingportions arranged in an 8-shape, and artificially displays Arabicnumerals “0” to “9”. The other groups 22 to 26 also have a constructionsimilar to that of the group 21. Numerals of six digits can be displayedby arranging a plurality of the respective groups 21 to 26 in atransversal direction. The group 21 is located in a least significantdigit, and the group 26 is located in a most significant digit.

Reference numeral 27 designates a unit mark portion which is one portionof the anode 2 and displays a unit “Km” of a running distance. Referencenumeral 28 a designates an ODO mark portion which is one portion of theanode 2 and displays a mark “ODO” showing that the digital type distancerecorder is set to a mode of an accumulating distance recorder.Reference numeral 28 b designates a trip mark portion which is oneportion of the anode 2 and displays a mark “TRIP” showing that thedigital type distance recorder is set to a mode of an interval distancerecorder. The ODO mark portion 28 a and the trip mark portion 28 a areselectively switched by an unillustrated switch so that only one ofthese mark portions is displayed. The display in the groups 21 to 26 isalso simultaneously switched. The unit mark portion 27, the ODO markportion 28 a and the trip mark portion 28 b are also light emittingportions.

FIG. 2 shows a circuit construction of such a digital type distancerecorder (luminous display unit) 100. Reference numeral 200 designates asensor for outputting a pulse signal in accordance with the number ofrotations of a wheel. Reference numeral 300 designates a counter forcounting an output (pulse number) from the sensor 200. Reference numeral400 designates an arithmetic control section constructed by amicrocomputer, etc. The arithmetic control section 400 calculates arunning distance from the counting number of the counter 300 by anarithmetic operation, and outputs a control signal so as to performdisplay in the above arithmetic operation, by the digital type distancerecorder 100. Reference numerals 500, 610 and 710 respectively designatea power circuit constructed by a battery mounted to a car, etc., aconstant electric current circuit section for obtaining a constantelectric current from the power circuit 500, and a switching section.The switching section 710 has switches 710 a to 710 g for supplying orinterrupting electric currents from constant electric current circuits610 a to 610 g of the constant electric current circuit section 610 tothe segments 21 a to 21 g so as to display a predetermined numeral onthe basis of commands from the arithmetic control section 400.

In FIG. 2, only the group 21 displaying the least significant digit isshown, and the other groups 22 to 26 are omitted. However, sections(constant electric current circuit sections 620 to 660 and switchingsections 720 to 760 which are not illustrated in the drawings)corresponding to the constant electric current circuit section 610 andthe switching section 710 are also respectively connected to the othergroups 22 to 26, and these groups 22 to 26 also display a predeterminednumeral on the basis of commands from the arithmetic control section400. In the following explanation, the group 21 is explained, butportions corresponding to the other groups 22 to 26 similarly hold trueunless it is emphatically said.

As mentioned above (see FIG. 7) with respect to a light emittingfrequency of each of the segments 21 a to 21 g in the display ofnumerals “0” to “9” in the group 21, the segment 21 c has a maximumlight emitting frequency of nine times, and the segment 21 e has aminimum light emitting frequency of four times. When it is supposed thata light emitting time of each of the numerals “0” to “9” is uniform, thelight emitting time of the segment 2 c is 2.25 times the light emittingtime of the segment 2 e. Thus, when a light emitting mode of each of thesegments 21 a to 21 g (light emitting portions) is regularly determinedso as to sequentially change the numerals from “0” to “9”, the lightemitting time can be presumed from the light emitting frequency of eachof the segments 21 a to 21 g calculated from the above light emittingmode.

Accordingly, as shown by a solid line A of FIG. 3, even when the lightemitting time of the segment 21 c is ten thousand hours as a half-life,the light emitting time of the segment 21 e is about 4444 hours andlight emitting luminance is about 82% of the original light emittingluminance. Therefore, when segments 21 c and 21 e in the group 21simultaneously emit light and display numerals “0”, “6” and “8”, thedifference in light emitting luminance between both the segments is 30%or more. Accordingly, since the difference in light emitting luminancecan be easily recognized, a problem exists in that a user has a feelingof physical disorder, etc. so that goods property is greatly damaged.

To solve this problem, in this embodiment, initial luminance of thesegment 21 e having a short light emitting time is set to be small incomparison with the segment 21 c having a long light emitting time withrespect to a using time of the digital type distance recorder (luminousdisplay unit) 100. Namely, the initial light emitting luminance of thesegment 21 e is set to about 80% of the normal light emitting luminance.Thus, characteristics of the light emitting luminance of the segment 21e are provided as shown by a broken line B of FIG. 3.

Accordingly, the difference in light emitting luminance between thesegments 21 c and 21 e is originally about 20%. Further, the lightemitting luminance of the segment 21 e is about 70% even when the lightemitting time of the segment 21 c reaches ten thousand hours as ahalf-life and the light emitting time of the segment 21 e becomes about4444 hours. Therefore, the difference in light emitting luminance doesnot change and is about 20% as it is. In the case of such a differencein light emitting luminance, it is difficult for a user to recognize thedifference in light emitting luminance between both the segments so thatthese light emitting luminances cannot be almost discriminated from eachother. Accordingly, goods property can be maintained without causing afeeling of physical disorder in the user.

To realize this, it is sufficient to adjust an electric current value byeach of the constant electric current circuits 610 a to 610 g of theconstant electric current circuit section 610. Since the light emittingluminance is proportional to the electric current value, the abovecharacteristics can be obtained by reducing the electric current valuefrom the constant electric current circuit 610 e supplying an electriccurrent to the segment 21 e.

As explained in the comparison of the segments 21 c and 21 e, the lightemitting time of each of the segments 21 a to 21 g is presumed from anexpected using time of the digital type distance recorder 100, and theindividual electric current values of the segments 21 a to 21 g, i.e.,the characteristics of the light emitting luminances may be set byadjusting the low electric current circuits 610 a to 610 g of theconstant electric current circuit section 610 such that the differencebetween high and low light emitting luminances lies within 30% of thehigh light emitting luminance among the light emitting luminances withinthis using time. However, as in this embodiment, it is possible toobtain effects of maintaining goods property without recognizing thedifference in light emitting luminance by comparing only maximum andminimum light emitting luminances and setting the characteristicsbetween these two light emitting luminances as mentioned above.

Further, in the above embodiment, the difference in light emittingluminance between the segment 21 e having a shortest light emitting timeand the segment 21 c having a longest light emitting time is restrainedby reducing the electric current value from the constant electriccurrent circuit 610 e supplying the electric current to the segment 21 ehaving a shortest light emitting time. However, reversely, it ispossible to easily understand that the difference in light emittingluminance between the segment 21 c having a longest light emitting timeand the segment 21 e having a shortest light emitting time may be alsorestrained by highly setting the electric current value from theconstant electric current circuit 610c supplying the electric current tothe segment 21 c having a longest light emitting time.

Such setting is similarly performed with respect to each of groups 22 to26 so that the difference in light emitting luminance in each of thegroups 22 to 26 can be restrained.

When no numeral “0” is displayed on an upper digit side, i.e., when“120” having no numerals “0” in upper three digits is displayed as ablank display instead of “000120” displaying numerals “0” in the upperthree digits in display of the numeral “120”, the light emitting time isshortened from the group 21 as a least significant digit to an upperdigit side. The light emitting time of the group 26 as a mostsignificant digit is shortest. Therefore, there is a possibility that aproblem similar to the difference in light emitting luminance in thesame digit is also caused between digits (groups 21 to 26).

In a construction for avoiding this problem, timing for starting lightemission in each digit in the digital type distance recorder 100 isassumed, and unillustrated constant electric current circuit sections620 to 660 supplying electric currents to the respective digits (groups22 to 26) are adjusted such that the difference between high and lowlight emitting luminances lies within 30% of the high light emittingluminance among the light emitting luminances. Namely, the electriccurrent value on the upper digit side is set to be sequentially reducedin comparison with the group 21, or the electric current value on alower digit side is set to be sequentially increased in comparison withthe group 26.

FIG. 4 shows a case in which the luminous display unit using the OLED 5(see FIG. 5) is utilized as a digital type travel speed meter 110 of adisplay unit for a vehicle. Namely, an anode 2 (see FIG. 5) is dividedinto three groups 21 to 23, and the group 21 is divided into sevensegments 21 a to 21 g as light emitting portions arranged in an 8-shape,and displays numerals “0” to “9”. The other groups 22 and 23 also have aconstruction similar to that of the group 21. Thus, numerals of threedigits can be displayed by arranging a plurality of the respectivegroups 21 to 23 in a transversal direction. The group 21 is located in aleast significant digit, and the group 23 is located in a mostsignificant digit. Reference numeral 29 designates a unit mark portionwhich is one portion of the anode 2 and displays the unit “Km/h” of atravel speed. The unit mark portion 29 is also a light emitting portion.

In the case of the travel speed meter 110, different from the distancerecorder 100, there is no regular property in the numeral displayed ineach digit. Accordingly, it is considered that it is not effective somuch to set the value of an electric current supplied to adjust thelight emitting luminance of each segment in each digit unit as mentionedin the preceding paragraph of the above embodiment.

However, it is known from an experience low in a general runningenvironment that a running opportunity of one hundred Km/h or more isvery small in comparison with running at a travel speed equal to orlower than one hundred Km/h. Namely, in the case of the travel speedmeter 110, when a numeric value in an upper digit is “0”, this numericvalue is not displayed. Accordingly, the light emitting time of thegroup 23 as a third digit is short in comparison with the light emittingtimes of the group 21 as a first digit and the group 22 as a seconddigit. Therefore, it can be estimated that differences in light emittingluminance are caused between the groups 21, 22 and the group 23. Incontrast to this, a running opportunity at a speed lower than ten Km/his small, and groups 21 and 22 are almost simultaneously displayed sothat there is no large difference in light emitting time between thegroups 21 and 22. Therefore, it can be estimated that no difference inlight emitting luminance is widened to such an extent that thisdifference can be recognized.

In such a construction, it is effective in maintenance of goods propertyto restrain the difference in light emitting luminance between thegroups 21, 22 and the group 23. To realize this, timing for startinglight emission in the most significant digit in the digital type travelspeed meter 110 is supposed, and an unillustrated constant electriccurrent circuit section supplying an electric current to each digit(groups 21 to 23) is adjusted such that the difference between high andlow light emitting luminances lies within 30% of the high light emittingluminance among the light emitting luminances. Namely, the electriccurrent value of the group 23 is set to be small in comparison with thegroups 21, 22, or the electric current values of the groups 21, 22 areset to be large in comparison with the group 23. Each electric currentvalue at this time is determined on the basis of an experience law, etc.However, as mentioned above, when the difference in light emittingluminance becomes a value corresponding to 30% of the high lightemitting luminance among the light emitting luminances or more, thedifference in light emitting luminance between both the groups can berecognized. Therefore, it is necessary to set the original difference inlight emitting luminance such that this original difference lies within30% of the high light emitting luminance among the light emittingluminances.

In each of the above embodiments, it is considered that display time islong in ensign portions of the unit mark portion 27, the ODO markportion 28 a, the trip mark portion 28 b (see FIG. 1) and the unit markportion 29 (see FIG. 4) in comparison with a display portion displayinga numeral so that a reduction in light emitting luminance is rapidlycaused. Therefore, there is a high possibility that the difference inlight emitting luminance between both the portions can be recognized. Todissolve this problem, it is sufficient to adjust the unillustratedconstant electric current circuit section for supplying electriccurrents to both the portions as mentioned above. Namely, an electriccurrent value in the display portion displaying a numeral is set to besmall in comparison with the ensign portion, or an electric currentvalue in the ensign portion is set to be large in comparison with thedisplay portion displaying a numeral. Each electric current value atthis time is determined on the basis of an experience law, etc. However,as mentioned above, when the difference in light emitting luminancebecomes a value corresponding to 30% of the high light emittingluminance among the light emitting luminances or more, the difference inlight emitting luminance between both the portions can be recognized.Therefore, it is necessary to set the original difference in lightemitting luminance such that this original difference lies within 30% ofthe high light emitting luminance among the light emitting luminances.

In each of the above embodiments, the distance recorder 100 and thetravel speed meter 110 are explained. However, the present invention canbe applied to a luminous display unit in which differences are caused inlight emitting time in plural light emitting portions in accordance withexistence of these light emitting portions. For example, the presentinvention can be also applied to a digital type clock and a digital typeengine tachometer.

In each of the above embodiments, the luminous display unit using theOLED is explained, but the present invention can be also applied to aluminous display unit using a self light emitting element in which thelight emitting luminance is reduced in accordance with the lightemitting time. For example, the present invention can be also applied toa fluorescent display tube (FLT) and a light emitting diode (LED).

However, a change in the light emitting luminance according to the lightemitting time (light emitting frequency) is notable in an organicelectroluminescence element. The present invention is suitable in aluminous display unit with such an organic electroluminescence elementas a self light emitting element.

In a display unit for a vehicle displaying numerals of plural digits, itis expected that this display unit is used for a long period such asseveral hundred thousand Km or several years. Accordingly, the change inlight emitting luminance is notable, and the present invention issuitable in a luminous display unit with such a display unit for avehicle as an object.

Industrial Applicability

As mentioned above, in the present invention, even when a luminousdisplay unit has plural light emitting portions by using a self lightemitting element reduced in light emitting luminance in accordance witha light emitting time and also has differences in light emitting time inthese light emitting portions, this luminous display unit can be usedfor a long time without recognizing the difference in light emittingluminance so that goods property can be maintained for a long time.

What is claimed is:
 1. A luminous display unit having plural light emitting portions by using a self light emitting element reduced in light emitting luminance in accordance with a light emitting time and having differences in light emitting time in their light emitting portions, and characterized in that, when a light emitting mode in said light emitting portions is regularly determined, said light emitting time is presumed from light emitting frequencies of said light emitting portions calculated from said light emitting mode, and the initial light emitting luminances are set to be different from each other in a light emitting portion having a large light emitting frequency and a light emitting portion having a small light emitting frequency during use of said luminous display unit so as not to cause a recognizable difference in light emitting luminance between both the light emitting portions during use.
 2. A luminous display unit according to claim 1, wherein said self light emitting element is an organic electroluminescence element.
 3. A luminous display unit according to claim 1, wherein said luminous display unit is a display unit for a vehicle displaying a numeral of plural digits.
 4. A luminous display unit having plural light emitting portions by using a self light emitting element reduced in light emitting luminance in accordance with a light emitting time and having differences in light emitting time in their light emitting portions, and characterized in that, when a light emitting mode in said light emitting portions is regularly determined, said light emitting time is presumed from light emitting frequencies of said light emitting portions calculated from said light emitting mode, and the initial light emitting luminances are set to be different from each other in a light emitting portion having a large light emitting frequency and a light emitting portion having a small light emitting frequency during use of said luminous display unit such that a difference in light emitting luminance caused between both the light emitting portions lies within 30% of a high light emitting luminance among the light emitting luminances during use.
 5. A luminous display unit having plural light emitting portions by using a self light emitting element reduced in light emitting luminance in accordance with a light emitting time and having differences in light emitting time in their light emitting portions, and characterized in that, when a light emitting mode in said light emitting portions is regularly determined, said light emitting time is presumed from light emitting frequencies of said light emitting portions calculated from said light emitting mode, and the initial light emitting luminance of a light emitting portion having a small light emitting frequency is set to be lower than that of a light emitting portion having a large light emitting frequency with respect to the light emitting portion having a large light emitting frequency and the light emitting portion having a small light emitting frequency during use of said luminous display unit such that a difference in light emitting luminance caused between both the light emitting portions lies within 30% of a high light emitting luminance among the light emitting luminances during use.
 6. A luminous display unit having plural light emitting portions by using a self light emitting element reduced in light emitting luminance in accordance with a light emitting time and having differences in light emitting time in their light emitting portions, and characterized in that the initial light emitting luminance of a light emitting portion having a long light emitting time and the light emitting luminance of a light emitting portion having a short light emitting time during use of said luminous display unit are set to be different from each other so as not to cause a recognizable difference in light emitting luminance between both the light emitting portions during use.
 7. A luminous display unit having plural light emitting portions by using a self light emitting element reduced in light emitting luminance in accordance with a light emitting time and having differences in light emitting time in their light emitting portions, and characterized in that the initial light emitting luminance of a light emitting portion having a long light emitting time and the light emitting luminance of a light emitting portion having a short light emitting time during use of said luminous display unit are set to be different from each other such that a difference in light emitting luminance caused between both the light emitting portions lies within 30% of a high light emitting luminance among the light emitting luminances during use.
 8. A luminous display unit having plural light emitting portions by using a self light emitting element reduced in light emitting luminance in accordance with a light emitting time and having differences in light emitting time in their light emitting portions, and characterized in that the initial light emitting luminance of a light emitting portion having a short light emitting time is set to be lower than that of a light emitting portion having a long light emitting time with respect to the light emitting portion having a long light emitting time and the light emitting portion having a short light emitting time during use of said luminous display unit such that a difference in light emitting luminance caused between both the light emitting portions lies within 30% of a high light emitting luminance among the light emitting luminances during use. 